Field of the Invention
The present disclosure relates to an apparatus for receiving a wireless power, a system for transmitting a wireless power including the same, and a method for controlling automatically an effective load resistance conversion ratio of a receiving end, and more particularly, to a technology of increasing a wireless transmission efficiency by adjusting a load resistance of the receiving end according to a distance change and a load change in a device that transmits power (or energy) wirelessly.
Description of the Related Art
A wireless power transmission system may be configured by a transmitter DC power supply, a transmitter resonant inverter, a transmission resonator, a reception resonator, a rectifier circuit, and a power converter. In order to get a high efficiency under constrains of a low coupling and a small resonator, the load resistance of a receiver should be optimized accordingly.
In addition, in addition to the transmission efficiency, a capability to transmit over a power amount required by the receiver may be also needed. Particularly, when the distance between a transmitter and the receiver increases, it is impossible to supply enough power to the receiver. A load resistance value as well as the distance may also influence on a power transmission amount. Consequently, in order to transmit a desired power to the receiver with a high efficiency, a load resistance value should be appropriately selected.
The problem is that it is difficult to arbitrarily change the load resistance value. That is, the load resistance is determined by a power requirement amount of a device which actually consumes a power, but is not a design parameter of a system. By using an impedance conversion circuit, it is possible to convert a value of the effective load resistance viewed from the reception resonator, and to improve performance.
However, the existing impedance conversion circuits cannot change arbitrarily an impedance conversion ratio but have a fixed conversion rate.
This is disadvantageous in that the performance may be degraded and the system may become unstable when the distance is changed or when the loading current is changed, although it is possible to achieve a performance optimization under a certain distance or a certain loading current condition.